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From "Aman Sinha (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-4181) Improve memory limit assignment for Sort operators
Date Wed, 09 Dec 2015 18:56:11 GMT
Aman Sinha created DRILL-4181:

             Summary: Improve memory limit assignment for Sort operators
                 Key: DRILL-4181
                 URL: https://issues.apache.org/jira/browse/DRILL-4181
             Project: Apache Drill
          Issue Type: Improvement
    Affects Versions: 1.4.0
            Reporter: Aman Sinha

Currently, the max_query_memory_per_node is divided among all the Sort operators in the query
plan, regardless of whether the Sort operators are executing at the same time.  Since Sort
is a blocking operator, the number of concurrent Sorts running is limited.  Thus, the Sort
on both sides of a MergeJoin could be concurrently executing but a Sort that occurs above
the MergeJoin cannot start until the MergeJoin produces a row which is only when both the
child Sorts have produced a row. 

Due to the conservative estimate, we have seen queries such as TPC-H Q8 with forced MergeJoin
run out-of-memory even with high max_query_memory_per_node.  This query plan has 15 Sort operators
and with max_width = 23,  max_query_memory_per_node = 20GB, each Sort gets only  63MB (20GB/(23*15)).
   We should improve the algorithm for computing the memory limit. 

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